Circular motion
Why is an object moving in a circle always accelerating?
One comparison at a time
Experiment with a guide
Distinguish constant speed from constant direction and compare the acceleration needed to turn.
Comparison 1 of 3
Observe the change in direction
We use a speed of 5 m/s and a radius of 3 m. Play or advance 0,25 s. Speed stays the same, but arrow v changes direction. That change is an acceleration.
Compare tangent arrow v with the arrow pointing to the centre. They have different directions.
You are exploring other values. You can continue freely or apply this comparison’s values again.
How to read this drawing
The point follows the dashed circle. R connects the centre to the point. Arrow v is tangent: it shows the direction of motion. The acceleration arrow points to the centre. The arrows indicate directions; length does not measure value. The drawing reframes the radius.
From drawing to graph
What changes? Let’s compare.
A line shows the relationship between quantities. The point marks your choice or the instant in the animation. First read the axis names and units.
One experiment at a time
Save. Change. Compare.
Save the current values, change one quantity and observe both lines on the same graph. The saved line is dashed. The attempt stays in this browser.
Compare the chosen values
What if… Try doubling the speed. What happens to acceleration? Then double the radius and compare.
What is happening?
Velocity changes direction at every instant. This change requires an acceleration pointing towards the centre.
Even when speed stays constant, the velocity vector changes direction. Any change in velocity is an acceleration. In uniform circular motion, this acceleration always points towards the centre of the path: it is called centripetal acceleration.
v — speed (m/s) · R — radius (m)
The model and its limits
Uniform circular motion: constant speed along a circular path in a plane. Arrows show directions; their visual lengths are not to scale with the quantities.